1. Field of the Invention
This invention relates to a method and an apparatus of driving a plasma display panel, and more particularly to a plasma display panel that is adaptive for improving brightness uniformity of an entire panel.
2. Description of the Related Art
Generally, a plasma display panel (PDP) radiates a fluorescent body using an ultraviolet with a wavelength of 147 nm generated upon discharge of an inactive mixture gas such as He+Xe, Ne+Xe or He+Ne+Xe, to thereby display a picture including characters and graphics. Such a PDP is easy to be made into a thin-film and large-dimension type. Moreover, the PDP provides a very improved picture quality owing to a recent technical development. Particularly, since a three-electrode, alternating current (AC) surface-discharge PDP has wall charges accumulated in the surface thereof upon discharge and protects electrodes from a sputtering generated by the discharge, it has advantages of a low-voltage driving and a long life.
Referring to FIG. 1, a discharge cell of the conventional three-electrode, AC surface-discharge PDP includes transparent electrodes 12Y and 12Z formed on an upper substrate 11 acting as a scan electrode and a sustaining electrode respectively, and an address electrode 17X formed on a lower substrate 16.
The transparent electrodes 12Y and 12Z are usually formed from indium-tin-oxide (ITO). There is metal bus electrodes 13 formed in each of the transparent electrodes 12Y and 12Z for reducing resistance. There are an upper dielectric layer 14 and a protective film 15 deposited on the upper substrate 11, where the transparent electrodes 12Y and 12Z are formed.
The address electrode 17X intersects the transparent electrodes 12Y and 12Z there are a lower dielectric layer 18 and a barrier rib 19 formed on the lower substrate on which the address electrode 17X is formed, and a fluorescent layer 20 is spread on the surface of the lower dielectric layer 18 and the barrier rib 19.
An inactive mixture gas such as He+Xe or Ne+Xe is injected into a discharge space defined between the upper and lower substrate 11 and 16 and the barrier rib 19 for a discharge.
Such a PDP drives one frame, which is divided into various sub-fields having a different discharge frequency, so as to express gray levels of a picture. Each sub-field is again divided into a reset period for having discharge generated uniformly, an address period for selecting a discharge cell and a sustain period for realizing the gray levels depending on the discharge frequency. For instance, when it is intended to display a picture of 256 gray levels, a frame interval equal to 1/60 second (i.e. 16.67 msec) is divided into 8 sub-fields. Each of the 8 sub-fields is divided into a reset period, an address period and a sustain period as mentioned above. Herein, the reset period and the address period of each sub-field are equal every sub-field, whereas the sustain period and its discharge frequency are increased at a ratio of 2n (wherein n=0, 1, 2, 3, 4, 5, 6 and 7) at each sub-field. In this way, since the sustain period becomes different in each sub-field, it is possible to realize the gray level of the picture.
PDP has its size large-dimentionalized like 40″, 50″, 60″ as compared with other flat panel displays PPD. Accordingly, because each of the electrodes 12Y, 12Z, 13, 17 of the PDP is long, a voltage drop due to the electrode length, which occurs in the central area, is relatively much more different from the voltage drop in the peripheral area. Further, because the PDP has discharge gas interposed into it with a lower pressure than atmospheric pressure, the strength applied to the substrates 11 and 16 in the central area where the upper/lower substrates 11 and 16 are only supported by the barrier ribs is different from the strength applied to the substrates 11 and 16 in the peripheral area where the upper/lower substrates 11 and 16 are joined by a sealant (not shown). As a result, a conventional PDP, as in FIG. 2, has the brightness of the central area 20% lower than that of the peripheral area, in both horizontal and vertical directions respectively though there is difference depending on the panel size.